<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .box1 {
    width: 200px;
    height: 200px;
    background-color: brown;
    /* 左右居中 */
    margin: 0 auto; 
  }
</style>
<body>

  <div class="box1">
    box1
  </div>
  
</body>
</html>